Mag and feeding problems

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Re: Mag and feeding problems

Postby GB30 » Sat Feb 09, 2019 6:58 pm

I'm new to the AR15 format so forgive me if I don't know or use correct technical language

I have a new BM450, overall I like the rifle but I'm having feed issues. When I purchashed the rifle I also ordered one spare mag from BM.

1st issue was was mainly with the extra mag, round would not go all the way to battery, or sometmes get stuck in the mag. could only get 4 rounds in mag, fifth round would need to be forced in. Found that the extra mag had another follower in the bottom for a spacer - looked like follower for a 308??? Sent spare mag back to bushmaster for replacement - both mags are the same now.

Current issue - With the bolt locked back if I insert a new mag the round most often pops out of mag. If I close the bolt before inserting the mag the round stays in the mag. But I still get intermitent stovepipes or double feeds.

Observations: I found that if I tap the mag so all the rounds go forward I can load the mag with the bolt locked back and it seems to cut down on misfeeds. I think that the rounds get shoved back do to the shock of firing the rifle so just getting them all forward to begin with isn't a good fix.

I found that the tab that locks the bolt back after last round is contacting (hanging over) the case of the round (see photos) and can cause it to tilt up or pop out altogether. I can see where this might cause misfeeds as the following round could actually be out of the feed lips as the bolt come back to battery???

The rounds do not seem to be sticking out the back of the mag. Also, no modifications have be done to the magazines or rifle.

Anyone had any issues like this?

thanks in advance, Gary
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Re: Mag and feeding problems

Postby Bmt85 » Thu Feb 14, 2019 2:34 pm

I haven't had to deal with that, yet, but have heard of it. Something is out if spec. I would take all other AR mags, doesn't matter the caliber, and check them. If the bolt catch looks like its protruding into other mags, I would trim it. If it's only protruding into that mag, then maybe trim it a little, or just don't run that mag.
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Re: Mag and feeding problems

Postby Hoot » Thu Feb 14, 2019 7:23 pm

If the round rises into position with enough nose up tilt, the rim gets tilted backward to where it can snag the BHO latch.
its a symptom not a cause. Try cutting a few turns off the bottom of the mag spring and/or squeezing the mag lips together a little. Most double stack mags have way too much spring force for a single stack application.

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Re: Mag and feeding problems

Postby timmy_the_large » Fri Oct 25, 2019 10:48 am

I highly suggest getting the Lancer L5 AMW AR-15 10 and 20 round mags https://www.midwayusa.com/product/2695117827 with Tromix Feed Followers https://tromix.com/product/center-feed-followers-for-lancer-mags/. I was having the same problems and this completely fixed it.
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Re: Mag and feeding problems

Postby Susquash » Sun Jan 12, 2020 5:18 pm

I recently put together a 450 Bushmaster upper for my AR-15. I experienced the same problem when checking feeding rounds through the action. Tried some pmag and it functioned fine. The magazine I have is a Stoner 5 round. About 30 minutes on the feed lips with a Dremel seems to have taken care of the problem as it now feeds well through the action. It sure does not say much for the quality control of the manufacturers with problems from so many different producers.
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Re: Mag and feeding problems

Postby Jlocutes » Thu Feb 20, 2020 7:40 pm

Is there a video to show you how to do polish the feed lips.. I have a 450 bushmaster pistol 7 1/2 inch barrel it seems to chambers around initially but upon firing sometimes it will load the next round sometimes it will not . if you pull the trigger the hammer just drops, I have to manually charge the next rd,I have a heavy buffer tube and spring in it I was having jamming issues with the AC are mags so I bought standard GIA 20 round mag‘s and that blue follower insert
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Re: Mag and feeding problems

Postby Bmt85 » Thu Mar 05, 2020 4:23 pm

You're just smoothing out the underside of the feedlips. You can use a dremel, sandpaper, emery cloth, file, whatever.

You have a 7.5" barrel, which short barrels can be finicky. Check the mag and make sure the rounds cycle through it smoothly, and don't bind up. If you have a problem with rounds stick the nose up too high (which may cause feeding issues), then try squeezing the feedlips together a little more from the middle of the mag. Does your pistol lock the bolt open on an empty mag? If not, it could be over or under gassed. You will probably have to try different buffer weights and springs. Only change one at a time, and one step different. (H2 to an H3 or H1). If it's really under gassed, you will need to open the gas port (last resort IMO). If it's really over gassed, you will need to run an adjustable gas block.

How many rounds are through the pistol? It could be it needs to break in. Run it extremely wet with oil until you getting running properly, then go light oil, or something else, like a dry lube, or grease, but start with a decent oil.

Unrelated question, but I have to ask, have you chronographed it?
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